The interpreter interface resembles that of the UNIX shell, but provides some
additional methods of invocation:

When called with standard input connected to a tty device, it prompts for
commands and executes them until an EOF (an end-of-file character, you can
produce that with Ctrl-D on UNIX or Ctrl-Z, Enter on Windows) is read.

When called with a file name argument or with a file as standard input, it
reads and executes a script from that file.

When called with a directory name argument, it reads and executes an
appropriately named script from that directory.

When called with -ccommand, it executes the Python statement(s) given as
command. Here command may contain multiple statements separated by
newlines. Leading whitespace is significant in Python statements!

When called with -mmodule-name, the given module is located on the
Python module path and executed as a script.

In non-interactive mode, the entire input is parsed before it is executed.

An interface option terminates the list of options consumed by the interpreter,
all consecutive arguments will end up in sys.argv – note that the first
element, subscript zero (sys.argv[0]), is a string reflecting the program’s
source.

Execute the Python code in command. command can be one or more
statements separated by newlines, with significant leading whitespace as in
normal module code.

If this option is given, the first element of sys.argv will be
"-c" and the current directory will be added to the start of
sys.path (allowing modules in that directory to be imported as top
level modules).

Search sys.path for the named module and execute its contents as
the __main__ module.

Since the argument is a module name, you must not give a file extension
(.py). The module-name should be a valid Python module name, but
the implementation may not always enforce this (e.g. it may allow you to
use a name that includes a hyphen).

Package names are also permitted. When a package name is supplied instead
of a normal module, the interpreter will execute <pkg>.__main__ as
the main module. This behaviour is deliberately similar to the handling
of directories and zipfiles that are passed to the interpreter as the
script argument.

Note

This option cannot be used with built-in modules and extension modules
written in C, since they do not have Python module files. However, it
can still be used for precompiled modules, even if the original source
file is not available.

If this option is given, the first element of sys.argv will be the
full path to the module file. As with the -c option, the current
directory will be added to the start of sys.path.

Many standard library modules contain code that is invoked on their execution
as a script. An example is the timeit module:

Execute the Python code contained in script, which must be a filesystem
path (absolute or relative) referring to either a Python file, a directory
containing a __main__.py file, or a zipfile containing a
__main__.py file.

If this option is given, the first element of sys.argv will be the
script name as given on the command line.

If the script name refers directly to a Python file, the directory
containing that file is added to the start of sys.path, and the
file is executed as the __main__ module.

If the script name refers to a directory or zipfile, the script name is
added to the start of sys.path and the __main__.py file in
that location is executed as the __main__ module.

Changed in version 2.5: Directories and zipfiles containing a __main__.py file at the top
level are now considered valid Python scripts.

If no interface option is given, -i is implied, sys.argv[0] is
an empty string ("") and the current directory will be added to the
start of sys.path.

When a script is passed as first argument or the -c option is used,
enter interactive mode after executing the script or the command, even when
sys.stdin does not appear to be a terminal. The
PYTHONSTARTUP file is not read.

This can be useful to inspect global variables or a stack trace when a script
raises an exception. See also PYTHONINSPECT.

Turn on hash randomization, so that the __hash__() values of str,
bytes and datetime objects are “salted” with an unpredictable random value.
Although they remain constant within an individual Python process, they are
not predictable between repeated invocations of Python.

Changing hash values affects the order in which keys are retrieved from a
dict. Although Python has never made guarantees about this ordering (and it
typically varies between 32-bit and 64-bit builds), enough real-world code
implicitly relies on this non-guaranteed behavior that the randomization is
disabled by default.

Force stdin, stdout and stderr to be totally unbuffered. On systems where it
matters, also put stdin, stdout and stderr in binary mode.

Note that there is internal buffering in file.readlines() and
File Objects (forlineinsys.stdin) which is not influenced
by this option. To work around this, you will want to use
file.readline() inside a while1: loop.

Print a message each time a module is initialized, showing the place
(filename or built-in module) from which it is loaded. When given twice
(-vv), print a message for each file that is checked for when
searching for a module. Also provides information on module cleanup at exit.
See also PYTHONVERBOSE.

Warning control. Python’s warning machinery by default prints warning
messages to sys.stderr. A typical warning message has the following
form:

file:line: category: message

By default, each warning is printed once for each source line where it
occurs. This option controls how often warnings are printed.

Multiple -W options may be given; when a warning matches more than
one option, the action for the last matching option is performed. Invalid
-W options are ignored (though, a warning message is printed about
invalid options when the first warning is issued).

Starting from Python 2.7, DeprecationWarning and its descendants
are ignored by default. The -Wd option can be used to re-enable
them.

Warnings can also be controlled from within a Python program using the
warnings module.

The simplest form of argument is one of the following action strings (or a
unique abbreviation) by themselves:

ignore

Ignore all warnings.

default

Explicitly request the default behavior (printing each warning once per
source line).

all

Print a warning each time it occurs (this may generate many messages if a
warning is triggered repeatedly for the same source line, such as inside a
loop).

module

Print each warning only the first time it occurs in each module.

once

Print each warning only the first time it occurs in the program.

error

Raise an exception instead of printing a warning message.

The full form of argument is:

action:message:category:module:line

Here, action is as explained above but only applies to messages that match
the remaining fields. Empty fields match all values; trailing empty fields
may be omitted. The message field matches the start of the warning message
printed; this match is case-insensitive. The category field matches the
warning category. This must be a class name; the match tests whether the
actual warning category of the message is a subclass of the specified warning
category. The full class name must be given. The module field matches the
(fully-qualified) module name; this match is case-sensitive. The line
field matches the line number, where zero matches all line numbers and is
thus equivalent to an omitted line number.

Turns all string literals into unicodes globally. Do not be tempted to use
this option as it will probably break your world. It also produces
.pyc files with a different magic number than normal. Instead, you can
enable unicode literals on a per-module basis by using:

These environment variables influence Python’s behavior, they are processed
before the command-line switches other than -E. It is customary that
command-line switches override environmental variables where there is a
conflict.

Change the location of the standard Python libraries. By default, the
libraries are searched in prefix/lib/pythonversion and
exec_prefix/lib/pythonversion, where prefix and
exec_prefix are installation-dependent directories, both defaulting
to /usr/local.

When PYTHONHOME is set to a single directory, its value replaces
both prefix and exec_prefix. To specify different values
for these, set PYTHONHOME to prefix:exec_prefix.

Augment the default search path for module files. The format is the same as
the shell’s PATH: one or more directory pathnames separated by
os.pathsep (e.g. colons on Unix or semicolons on Windows).
Non-existent directories are silently ignored.

The default search path is installation dependent, but generally begins with
prefix/lib/pythonversion (see PYTHONHOME above). It
is always appended to PYTHONPATH.

An additional directory will be inserted in the search path in front of
PYTHONPATH as described above under
Interface options. The search path can be manipulated from
within a Python program as the variable sys.path.

If this is the name of a readable file, the Python commands in that file are
executed before the first prompt is displayed in interactive mode. The file
is executed in the same namespace where interactive commands are executed so
that objects defined or imported in it can be used without qualification in
the interactive session. You can also change the prompts sys.ps1 and
sys.ps2 in this file.

Set this to a non-empty string to cause the time module to require
dates specified as strings to include 4-digit years, otherwise 2-digit years
are converted based on rules described in the time module
documentation.